1. Field of the Invention
The present invention relates to a method of fabricating semiconductor devices, and more particularly, to a method of forming a metal nitride film by chemical vapor deposition (CVD) where a metal source and a nitrogen source are used as a precursor, and a method of forming a metal contact and a capacitor of a semiconductor device using the above method.
2. Description of the Related Art
A barrier metal layer, which prevents mutual diffusion or chemical reaction between different materials, is indispensable to stabilize the contact interfaces of semiconductor devices. In general, a metal nitride such as TiN, TaN or WN has been widely used as the barrier metal layer of semiconductor devices. Here, TiN is a representative example among the above metal nitrides.
However, when the metal nitride film such as TiN is fabricated by sputtering, its application to highly integrated semiconductor devices is not appropriate, due to low step coverage. For an example, FIGS. 9A and 9B show the cross-section of a via contact for connection between metal wiring. FIGS. 9A and 9B show a simple via contact and an anchor via contact, respectively. The formation processes thereof are as follows. A first metal layer 30 composed of aluminum (Al) is formed on a semiconductor substrate 20. A TiN film 40 is formed as a capping film on the resultant structure by sputtering, and then an interlayer insulative film 50 or 51 is deposited. A contact hole is formed by etching the interlayer insulative film 50 or 51 on the first metal layer 30. In FIG. 9B, the step of forming an anchor A by wet etching is added. After Ti as an adhesive layer and TiN 60 or 61 as a barrier metal layer is deposited, a tungsten (W) plug 70 or 71 is formed to fill the contact hole, by CVD. Thereafter, tungsten at the upper portion is removed by chemical mechanical polishing or etch-back, and then a second metal layer is deposited on the resultant structure, thereby completing the connection between metal wiring. However, this last step is not shown.
Here, in a conventional method, the TiN film 60 or 61, being the barrier metal layer, is deposited by sputtering, with inferior step coverage. Here, the thickness of a TiN film on the bottom, corner and anchor A of the contact hole is reduced, with an increase in the aspect ratio of the via. Accordingly, at a thin portion, Ti or Al combines with fluorine remaining in tungsten source gas WF6 during tungsten deposition being a subsequent process, and thus an insulative film X is formed of TiFx or ALFx, leading to a contact failure.
When the contact failure is avoided by increasing the deposition time to increase the thickness of the TiN film 60 or 61, the thickness of the TiN film increases only at the upper portion of the contact hole, and the upper portion of the contact hole is narrowed or blocked. Thus, voids are likely to be generated upon subsequent tungsten deposition. A process with improved step coverage is required to apply TiN to a contact with a high aspect ratio. Accordingly, a process for fabricating a metal nitride film using CVD (hereinafter called a CVD-metal nitride film) has been developed as a next generation process.
A general process for forming a CVD-metal nitride film uses a metal source containing chlorine (Cl), e.g., a precursor such as titanium chloride TiCl4. The CVD-metal nitride film using TiCl4 as the precursor has a high step coverage of 95% or higher and is quickly deposited, but Cl remains in the metal nitride film as impurities. The Cl remaining as impurities in the metal nitride film causes corrosion of metal wiring such as Al and increases resistivity. Thus, the Cl content in the metal nitride film must be reduced and the resistivity must be lowered, by deposition at high temperature. That is, in the CVD-metal nitride film process using the metal source such as TiCl4, a deposition temperature of at least 675xc2x0 C. is required to obtain resistivity of 200 xcexcxcexa9-cm or less. However, a deposition temperature of 600xc2x0 C. or more exceeds thermal budget and thermal stress limits which an underlayer can withstand. In particular, when the metal nitride film is deposited on an Si contact or a via contact with an Al underlayer, a deposition temperature of 480xc2x0 C. or lower is required, so that a high temperature CVD-metal nitride film process cannot be used.
A low temperature deposition CVD-metal nitride film process is possible, by adding MH (methylhydrazine, (CH3)HNNH2) to the metal source such as TiCl4, but this method has a defect in that step coverage is decreased to 70% or lower.
Another method capable of low temperature deposition is to form a MOCVD-metal nitride film using a metalorganic precursor such as TDEAT (tetrakis diethylamino Ti, Ti(N(CH2CH3)2)4), or TDMAT (tetrakis dimethylamino Ti, Ti(N(CH3)2)4). The MOCVD-metal nitride film has no problems due to Cl and can be deposited at low temperature. However, the MOCVD-metal nitride film contains a lot of carbon (C) as impurities, giving high resistivity, and has inferior step coverage of 70% or less.
A method of forming a metal nitride film using atomic layer epitaxy (ALE) has been tried as an alternative to deposition, in order to overcome the problems due to Cl. However, the ALE grows the metal nitride film in units of an atomic layer using only chemical absorption, and the deposition speed (0.25 A/cycle or less) is too slow to apply the ALE to mass production.
A TiN film is also used as the electrode of a semiconductor capacitor. In particular, the TiN film is usually used in a capacitor which uses tantalum oxide (Ta2O5) as a dielectric film. Semiconductor capacitors, which use the TiN film as an electrode, also have the above-described problems.
That is, in order for a semiconductor capacitor to have a high capacitance per unit area of a semiconductor substrate, its electrode is designed three-dimensionally, as in cylindrical capacitors. Hence, the shape of the semiconductor capacitor is so complicated that it is critical to guarantee step coverage of deposited materials as its electrode. Accordingly, a TiN electrode formed by CVD using a Cl-containing metal source having an excellent step coverage as a precursor has been used as the electrode of a capacitor. However, as described above, the CVDed TiN film provokes corrosion of metal wiring and gives high resistivity, due to a high concentration of Cl, resulting in a degradation in the leakage current characteristics of a capacitor.
To solve the above problems, an objective of the present invention is to provide a method of forming a metal nitride film, which gives excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity.
Another objective of the present invention is to provide a method of forming a metal contact having a barrier metal layer which has excellent step coverage even at a high deposition speed and a low temperature, low impurity concentration, and low resistivity, by applying the metal nitride film formation method to a metal contact of a semiconductor device.
Still another objective of the present invention is to provide a method of forming a capacitor which gives excellent step coverage, low impurity concentration and low resistivity, using the metal nitride film formation method.
Accordingly, to achieve the first objective, there is provided a method of forming a metal nitride film using chemical vapor deposition (CVD) in which a metal source and a nitrogen source are used as a precursor. In this method, first, a semiconductor substrate is introduced into a deposition chamber, and the metal source flows into the deposition chamber. After a predetermine time, the flow of the metal is stopped, and a purge gas is introduced into the deposition chamber. After a predetermined time, the purge gas is cut off and the nitrogen source gas flows into the deposition chamber to react with the metal source adsorbed on the semiconductor substrate. Again, after a predetermined time, the nitrogen source gas remaining in the deposition chamber is removed by cutting off the inflow of the nitrogen source gas and flowing the purge gas into the deposition chamber. Thus, the metal nitride film is formed on the semiconductor substrate.
In the metal nitride film formation method of the present invention, a gas inflow cycle of a sequence of the metal source, the purge gas, the nitrogen source, and the purge gas, can be repeated until a metal nitride film having a desired thickness is obtained.
Here, a titanium nitride film TiN can be formed by using TiCl4 (titanium chloride), TiCl3 (titanium chloride), TiI4 (titanium iodide), TiBr2 (titanium bromide), TiF4 (titaniumfluoride), (C5H5)2TiCl2 (bis(cyclopentadienyl)titanium dichloride), ((CH3)5C5)2TiCl2 (bis(pentamethylcyclopentadienyl) titanium dichloride), C5H5TiCl3 (cyclopentadienyltitanium trichloride), C9H10BCl3N6Ti (hydrotris (1-pyrazolylborato) trichloro titanium), C9H7TiCl3 (indenyltitanium trichloride), (C5(CH3)5)TiCl3 (pentamethylcyclopentadienyltitanium trichloride), TiCl4 (NH3)2 (tetrachlorodiaminotitanium), (CH3)5C5Ti(CH3)3 (trimethylpentamethylcyclopentadienyltitanium), TDEAT or TDMAT as the metal source, and using NH3 as the nitrogen source. Alternatively, the tantalum nitride film TaN can be formed using a material selected from the group consisting of TaBr5 (tantalum bromide), TaCl5 (tantalum chloride), TaF5 (tantalum fluoride), TaI5 (Tantalum iodide), and(C5(CH3)5)TaCl4 (pentamethylcyclopentadienyltantalum tetrachloride), as the metal source, and using NH3 as the nitrogen source.
Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
Preferably, 1-5 sccm of the metal source flows into the deposition chamber for 1 to 10 seconds, 5-200 sccm of the nitrogen source flows thereinto for 1 to 10 seconds, and 10-200 sccm of the purge gas flows thereinto for 1 to 10 seconds.
Also, an atmospheric gas such as Ar, He and N2 can be continuously flowed into the deposition chamber, to maintain a constant pressure in the deposition chamber.
Meanwhile, when the TiN film is formed using TDEAT or TDMAT as the metal source, it is preferable to maintain the pressure in the deposition chamber to be 0.1-10 torr and the deposition temperature to be between 250xc2x0 C. and 400xc2x0 C. When materials other than TDEAT and TDMAT are used as the metal source, the pressure in the deposition chamber is maintained to be 1 to 20 torr and the deposition temperature is maintained to be between 400xc2x0 C. and 500xc2x0 C.
To achieve the second objective, there is provided a method of forming a metal contact of a semiconductor device, wherein a first metal layer, an interlayer insulative film, a contact hole, a barrier metal layer, a metal plug, and a second metal layer are sequentially formed on a semiconductor substrate. A process for forming the barrier metal layer is as follows. A metal source flows into the semiconductor substrate having the interlayer insulative film in which the contact hole exposing the first metal layer is formed. The metal source is adsorbed to the resultant structure. After a while, the metal source remaining in the deposition chamber is removed by cutting off the inflow of the metal source and flowing a purge gas into the deposition chamber. After a predetermined time, the purge gas is cut off, and a nitrogen source flows into the deposition chamber. The nitrogen source reacts with the metal source adsorbed on the semiconductor substrate, to thus form a metal nitride film, being the barrier metal layer, on the exposed first metal layer and the contact hole. Again, after a while, the nitrogen source remaining in the deposition chamber is removed by cutting off the inflow of the nitrogen source and flowing the purge gas into the deposition chamber.
The barrier metal layer formation process can be repeated until a barrier metal layer having a desired thickness is obtained.
Here, a titanium nitride film TiN as the barrier metal layer is formed by using a material selected from the group consisting of TiCl4, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT and TDMAT as the metal source, and using NH3 as the nitrogen source. Alternatively, the tantalum nitride film TaN as the barrier metal layer is formed using a material selected from the group consisting of TaBr5, TaCl5, TaF5, TaI5, and (C5(CH3)5)TaCl4 as the metal source, and NH3 as the nitrogen source.
Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
The flow amounts and flow times of the metal source, nitrogen source, and purge gas flowing into a deposition chamber are within the same ranges as in the above-mentioned method of forming the metal nitride film.
Also, in order to maintain a constant pressure within the deposition chamber while forming a barrier metal layer, the pressure within the deposition chamber is kept at about 0.1 to 10 torr when TDEAT or TDMAT is used as the metal source, and about 1 to 20 torr when materials other than TDEAT and TDMAT are used as the metal source. The constant pressure is maintained using an atmospheric gas such as Ar, He, or N2.
It is preferable that a deposition temperature upon the formation of the barrier metal layer is about between 250xc2x0 C. and 400xc2x0 C. when TDEAT or TDMAT is used as the metal source, and between 400xc2x0 C. and 500xc2x0 C. when materials other than TDEAT and TDMAT are used as the metal source.
To achieve the third objective, there is provided a method of forming a semiconductor capacitor, wherein a lower conductive layer, a dielectric film and an upper conductive layer are sequentially formed on the underlayer of a semiconductor substrate. In a process for forming the lower and/or upper conductive layer, a semiconductor substrate on which an underlayer or a dielectric film is formed is introduced into a deposition chamber, and a metal source flows into the deposition chamber. The metal source is chemically and physically adsorbed onto the substrate. After a predetermined period of time, the metal source is purged from the deposition chamber. After a predetermined period of time, a nitrogen source flows into the deposition chamber, and is chemically and physically adsorbed onto the substrate. The adsorbed metal source and nitrogen source are reacted to form a metal nitride film on the substrate. After another predetermined period of time, the nitrogen source is purged from the deposition chamber.
The step of forming a metal nitride film can be repeated until a lower and/or upper conductive layer having a desired thickness is obtained.
Here, when Ti is used, the metal source used to form the lower and/or upper conductive layer is selected from the group consisting of TiCl4, TiCl3, TiI4, TiBr2, TiF4, (C5H5)2TiCl2, ((CH3)5C5)2TiCl2, C5H5TiCl3, C9H10BCl3N6Ti, C9H7TiCl3, (C5(CH3)5)TiCl3, TiCl4(NH3)2, (CH3)5C5Ti(CH3)3, TDEAT and TDMAT. When Ta is used, the metal source is selected from the group consisting of TaBr5, TaCl5, TaF5, TaI5, and (C5(CH3)5)TaCl4. The nitrogen source is NH3.
Also, it is preferable that the purge gas is an inert gas such as Ar or N2.
The flow amounts and inflow times of a metal source, a nitrogen source and a purge gas flowing into the deposition chamber are within the same ranges as those in the metal nitride film formation method according to the present invention.
Also, in order to maintain a constant pressure within the deposition chamber while forming a lower and/or upper conductive layer, the pressure within the deposition chamber is maintained to be about 0.1-10 torr when TDEAT or TDMAT is used as a metal source, and the pressure within the deposition chamber is maintained to be about 1-20 torr when materials other than TDEAT and TDMAT are used as the metal source. The constant pressure is maintained by the use of an atmospheric gas such as Ar, He or N2.
Preferably, when TDEAT or TDMAT is used as the metal source, the deposition temperature in each of the steps for forming a lower conductive layer and/or an upper conductive layer is between 250xc2x0 C. and 500xc2x0 C. Also, preferably, when other materials are used as the metal source, the deposition temperature in each of the steps for forming a lower conductive layer and/or an upper conductive layer is between 400xc2x0 C. and 500xc2x0 C.
According to the present invention, a metal nitride film having low resistivity of 200xcexcxcexa9-cm or less and a low content of Cl can be obtained even with excellent step coverage. Also, a CVD-metal nitride film can be formed at a temperature of 500xc2x0 C. or less even at a deposition speed of about 20 A/cycle, so that the deposition speed of the present invention is higher than that of a metal nitride film formation method using ALE having a growth speed of 0.25 A/cycle. A capacitor, in which a metal nitride film formed by the method according to the present invention is used as a lower and/or upper conductive layer, has excellent step coverage and excellent leakage current characteristics.